Save your game and go talk to the innkeeper.
He will offer you a piece of information for 10,000 Gil - that you can then sell for a profit to another person in town. People will offer you from 25,000 to 100,000 Gil.
You will get a hint as to who the person will be.
If the hint is "It's the last person you'd expect" then just talk to the innkeeper again and get the 100,000 Gil! If not, just reload the game until you get the chance to make that 90,000 Gil profit.
A good way to do so is to equip the Treasure Hunt GG, and use the Mug command instead of Attack. Even if you don't steal anything, you will gain double the APs. Combine that with the AP Egg for super fast Abilities levelling up.